Respuesta :

√-16 / [(1+i)+(6+3i)]=
4i/[(1+i)+(6+3i)]=
4i/(7+4i)=
4i/(7+4i) (7-4i)/(7-4i)=
4i(7-4i) / [(7+4i)(7-4i)]=
(28i-16i²) / (49-16i²)=
(28i+16) / (49+16)=
(28i+16) /65

Remember:
i=√-1
i²=-1

Answer:√-16 / [(1+i)+(6+3i)]= (28i+16) /65